Disruption tolerant networks (DTNs) is a research area aiming at developing network communication when connectivity is intermittent and prone to disruptions. The disruptions in DTNs occur due to many factors, such as node mobility, physical obstacles, depleted energy, and low node density. In such environments, data can be delivered by mobile nodes, which store, carry, and then forward data towards destinations. Unfortunately, many mobility scenarios depend on untethered devices with limited energy supplies. Therefore, power management schemes are highly needed in such networks in order to extend the network lifetime and to avoid degraded network connectivity.A wireless interface is one of the largest consumers of energy in energy-limited devices and it can work in four different modes: listening, transmitting, receiving, and sleeping. Wireless interfaces consume a significant amount of energy even in the idle "listening mode". Therefore, a significant amount of energy can be saved by allowing nodes to put their wireless interfaces into sleeping mode. In DTNs, nodes need to discover neighbors to establish communication. Searching for neighbors in sparse DTNs can consume a large amount of power compared to the power consumed by infrequent data transfers. Thus, designing such power management schemes is challenging, because nodes need to know when to sleep, to save power, and when to wake up to search for neighbors. Ideally, power management schemes should not reduce network connectivity opportunities that would negatively affect the overall performance of the network.In this thesis, we first present a power management scheme called Multi-Radio (MR) scheme, in which nodes are equipped with two complementary radios: a high-power radio and a lowpower radio. In this scheme, energy can be conserved by using a low-power radio to discover communication opportunities with other nodes and waking up a high-power radio to undertake the data transmission. In addition, we investigate the impact of different node mobility patterns on the MR scheme: we study the effects of Random Waypoint, Manhattan, Message Ferry, Human and Zebra mobility models on the MR scheme. Finally, we introduce a Multi-Acoustic Modem power management scheme for sparse shallow underwater networks, in which nodes are equipped with two acoustic modems, low-power acoustic modem for neighbor discovery and high-power acoustic modem for data exchange.